The present invention relates to an automatic document feeding device provided on a recording apparatus such as an electrophotographic copying machine and on an image reading apparatus, and more particularly to a document stacker where single-sided or double-sided image documents are stacked.
As a device capable of feeding a document on which images are recorded efficiently even under the unmanned condition in an electrophotographic copying machine or in a recording apparatus such as a recorded image reading apparatus, there has already been provided an automatic document feeder (ADF).
In recent copying machines, in particular, high copying process speed, high document conveyance speed of ADF, and shortened time for document change and for recording sheet feeding for an improvement of copy productivity have been attained for the purpose of elevating copying efficiency.
In a copying machine equipped with a conventional automatic document feeding device, time for feeding a recording sheet is shortened in a manner wherein passage of the trailing edge of a document is detected by a document trailing edge detecting means provided at the feeding section in the main body of the automatic document feeding device, and detection signals therefrom are sent to the main body of the copying machine, and thereby the following recording sheet is fed preliminarily from a sheet feeding device in the copying machine.
The preliminary sheet feeding mentioned above is especially effective because of a long sheet feeding path when a copying machine is of structure wherein a sheet-feeding cassette containing recording sheets and a stacker for double-sided copying are positioned to be far from a transfer unit in an image forming section.
However, when the last document is fed and detection signals for passage of the trailing edge of the last document (no following document) are sent, a sheet feeding device in the main body of the copying machine receives the signals and operates to start preliminary feeding for a following recording sheet despite no following document existing. Therefore, it is necessary to return the recording sheet fed preliminarily.
The invention further relates, in particular, to an improvement of a sheet feeding section wherein documents stacked on a document stacker are fed out by a feed-out means, one sheet of document is separated from the documents by a separating means to be fed, the separated document is aligned by a pair of registering rollers for standby thereof and then is fed to an image reading section.
Further, a reversible automatic document feeder (R-ADF) that is represented by the aforementioned ADF equipped with a function of turning over a document has been put to practical use for a copying machine capable of copying each image on a document (double-sided document) having recorded images on its both sides on one side or on both sides of a recording material or for an image reading apparatus capable of reading and recording the images mentioned above.
Document conveyance on a document placing glass (a platen glass) in the reversible automatic document feeder (R-ADF) mentioned above is carried out by a conveyance belt which is wound around a conveyance driving roller and a conveyance driven roller to be capable of running regularly and reversely.
As a means of stopping conveyance for positioning a document conveyed by the above-mentioned conveyance belt at the predetermined location on a platen glass, there are available a method wherein a document is caused to hit a stopper to be positioned and a method wherein a sensor detects an edge of a document pass and a timer or a counter is used for counting time to control the position of the document.
As a method for stopping a document by means of a conveyance belt in the document feeder mentioned above, there has generally been used a method wherein an edge of a document hits a stopper plate affixed at an end of a platen glass. The method, however, has a problem that it takes time before a document is stopped, an accuracy of a stopped position for a document is unstable, and an edge of a document is damaged.
For solving the problem mentioned above, there is available a method wherein a document is controlled to stop without hitting a stopper plate during automatic conveyance of the document. In this method, however, a stopping position of a document varies exceedingly, which has not been solved yet.
Further, the invention relates to an automatic document feeding device having a single-sided image document conveyance (ADF) mode wherein a sheet of single-sided or double-sided image document is separated from those stacked on a document stacker and is fed to an image reading section, and then it is ejected, after being read, onto a delivery tray, or a double-sided image document reversing/conveying (R-ADF) mode wherein a document whose image has been read is turned over and is conveyed again to an image reading section.
In a recent copying machine wherein a copying speed has been increased for enhancing copying efficiency and thereby a document conveyance speed has also been increased (approx. 1000-1200 mm/sec) so that a document is ejected onto a delivery tray at that speed, in particular, documents are ejected onto the delivery tray irregularly or they jump out of the delivery tray.
Various suggestions have been made as a measure for the problem mentioned above. For example, what is disclosed in Japanese Patent Publication Open to Public Inspection No.61-178363(hereinafter referred to as Japanese Patent O.P.I. Publication) (conventional example 1) is characterized to have a sheet-ejecting roller decelerating means wherein a sheet sensor that detects a pass of a document is provided immediately before a sheet-ejecting roller, and rotating speed of the sheet-ejecting roller is decreased when the trailing edge of a document is detected by the sheet sensor.
Further, what is disclosed in Japanese Patent O.P.I. Publication No. 62-12564conventional example 2) is equipped with a switching means capable of changing rotating speed of a document-ejecting means to the first ejecting speed that is the same as the document conveyance speed or to the second ejecting speed that is lower than the first ejecting speed.
On the other hand, in Japanese Patent O.P.I. Publication No.62-70159(conventional example 3), it is disclosed that ejection speed is reduced by a brake and a clutch when the trailing edge of a document to be ejected is detected by a sensor.
In Japanese Patent O.P.I. Publication No. 62-111854(conventional example 4), it is disclosed that conveyance speed is kept to be slower for a certain period of time after the trailing edge of a document is detected.
Furthermore, in Japanese Patent O.P.I. Publication No. 03-152055(conventional example 5), there are disclosed a low speed ejecting roller and a pressing member capable of being brought into pressure-contact with or released from the low speed ejecting roller.
Further, a problem of skewed copy caused by a document skewed in the course of conveyance thereof and a problem that an ejected document falls out of an apparatus due to down-sizing are remain unsolved.
The proposals mentioned above have various features and are effective as a measure. However, they are not necessarily free of problems. For example, in the conventional examples 1 and 4, when a conveyance belt and a sheet-ejecting roller are driven by a single motor, lowered speed of the motor causes also a conveyance belt to be slow in speed, making it difficult for the following document to be conveyed onto a platen glass, thus copying productivity can not be enhanced. When an additional motor is used unlike the conventional example 1 employing only one motor, it is not advantageous in terms of cost. In the conventional example 2, gear train for driving is complicated and it requires a large number of gears, resulting in a high cost.
In the conventional example 3, a combination of a brake and a clutch is complicated and it requires many parts, resulting in high cost. Further, durability of a clutch is also doubtful.
In the conventional example 4, a means for controlling document conveyance speed is complicated and expensive, which is a disadvantage.
In the conventional example 5, a pressing member and a claw for switching between sheet-reversing and sheet-ejecting require respectively different driving sources (solenoid or the like), causing problems of timing control and high cost.
As stated above, it is necessary to reduce a sheet-ejecting speed for the purpose of preventing that documents are ejected irregularly onto a delivery tray. It is confirmed experimentally that a linear speed at which the documents can be ejected regularly onto a delivery tray positioned almost horizontally is not more than 400 mm/sec. However, when a total automatic document feeder is driven at a document conveyance speed of not more than 400 mm/sec, a ratio of Opm (number of fed documents per minute in ADF) to Cpm (number of copies per minute in a copying machine) is reduced. When Cpm on the main body side of a copying machine is raised to be high speed (for example, 50-70 sheets per minute for A4 size), it is desired to attain copying productivity of 100% by achieving the high number of documents conveyed matching with the Cpm. For the purpose of enhancing further the aforesaid linear speed and still attaining regular sheet alignment, a delivery tray has been inclined so that a document ejected out of an apparatus may climb along the inclined delivery tray to be reduced in its speed. In this case, the total height of ADF is increased, and when the ADF is structured to be opened toward an operator, a wall side located on the back side of a copying machine hits articles. For avoiding this, therefore, an excessive space needs to be provided on the rear side of the copying machine, resulting in problem of an increase of a floor space.
When a document of the maximum size (for example, A3 size or 11.times.17 in. size) out of documents ejected from the aforementioned ejection section is ejected, it slides on the surface of a delivery tray and jumps excessively to be scattered irregularly on the delivery tray, or it falls from the delivery tray, and sometimes, succeeding ejected documents hit preceding stacked documents due to the document of the maximum size aligned irregularly, causing defective document ejection.
Furthermore, in R-ADF wherein a double-sided image document is fed into an ejection section from a conveyance section, turned over and is conveyed again onto a platen glass, there is a fear that the document is skewed in the course of conveyance to fail to be located at the right image forming position. For this reason, a document has been pushed against a document end stopper (scale plate), which, however, caused a problem that a leading edge of a document is damaged and a document stopping means is complicated. In the case of an automatic document feeding device having no document positioning stopper on the one end on the surface of a platen glass, in particular, a defective position for document image reading caused by the skewed document mentioned above is observed remarkably.